Method and machine for producing teeth and threads on enveloping members



E. WILDHABER METHOD AND MACHINE FOR PRODUCING TEETH AND THREADS ON ENVELOPING MEMBERS Jan. 10, 1961 8 Sheets-Sheet 1 Filed Feb. 24, 1958 2,967,461 RODUCING TEETH AND THREADS 0N ENVELOPING MEMBERS Jan. 10, 1961 E. WILDHABER METHOD AND MACHINE FOR P 8 Sheets-Sheet 2 Filed Feb. 24, 1958 FIG. 9

INVENTOR. Eru.. ,.,t WM

Jan. 10, 1961 E. WILDHABER 2,967,461

METHOD AND MACHINE FOR PRODUCING TEETH AND THREADS 0N ENVELOPING MEMBERS 8 Sheets-Sheet 3 Filed Feb. 24. 1958 I32 FIG. [4 v Ifl6 ' INVENTOR.

FIG/8 Jan- 1 1961 E. WILDHABER 2,967,461

METHODAND MACHINE FOR PRODUCING TEETH AND THREADS ON ENVELOPING MEMBERS Filed Feb. 24, 1958 8 Sheets-Sheet 4 INVENTOR? 5M4- WM FIG.24

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FIG. 34

INVENTOR.

METHOD AND MACHINE FOR PRODUCING TEETH AND THREADS 6N ENVELOPING MEMBERS Ernest Wildhaher, Brighton, N.Y. (124 Summit Drive, Rochester 20, N.Y.)

Filed Feb. 24, 1958, Ser. No. 716,957

30 Claims. (Cl. 9il4) The present invention relates to methods and machines for producing teeth and threads of enveloping members, such as wormgears, enveloping worms, enveloping rotary laps, enveloping threaded grinding members, and the like. The teeth and threads of such enveloping members have varying distances from the axis of the respective member, on their sides and usually also on their outside surfaces, and generally a distance at their ends larger than the distance at the middle portion.

One object of the present invention is to devise a method and machine for producing the enveloping worm gearing disclosed in my application Serial No. 701,792, filed December 10, 1957. Either the wormgear or the worm or both may be produced thereby.

Hitherto it has been customary in cutting any wormgear to provide a tool, especially a hob, that represents the worm and that has approximately the diameter of the worm that is to mesh with the wormgear. Such hobs are very costly especially when large. A further object is to devise an efiicient method and machine for producing wormgears, as well as throated or non-helical worms, with standard tools that are not specific to a given job, and that can be used for a wide range of jobs of a given pitch. A related aim is to bring the production of wormgears and throated worms to the general level of the generation of spur gears and helical gears, where only the normal pitch matters and no special tools are required.

A further object is to provide a method and machine for efiiciently and accurately cutting a wormgear to mesh with a multiple threaded helical worm with a standard generating tool including a single-threaded hob.

A still other aim is to provide a method and machine for cutting a throated and non-helical worm, whose wormgear contains helical teeth or straight teeth, in a generating operation with a standard tool or cutter.

An enveloping worm to mesh with a helical gear or spur gear may also be embodied as a rotary lap or a rotary grinding member. Such enveloping laps and grinding members have a long duration of contact with the workpiece, with many threads or teeth in simultaneous contact, as desired for good and rapid equalization and correction of the teeth.

A further aim is to devise a method and machine for truing such laps and grinding members with reciprocatory tools that gradually sweep the entire thread surfaces.

A still other aim is to devise a method and machine for producing a toothed member conjugate to an imaginary internal member whose inside diameter is smaller than the smallest root diameter of said member.

Further a machine shall be devised for producing enveloping or non-helical teeth and threads on a workpiece with standard tools, in a process employing feed about and along an axis angularly disposed to and offset from the axis of the workpiece, where the feed rate along said axis has a varying ratio to the feed rate about said axis. Also a machine of the named character shall be devised that requires neither special tools tied .up with a given job nor special cams tied up therewith, and where a wide atent C 2 range of jobs can be handled without special equipment.

Other objects will appear in the course of the specification and in the recital of the appended claims.

The objects may be attained singly or in any combination.

In the drawings:

Fig. 1 is a diagrammatic plan view of an enveloping worm and wormgear, such as may be produced according to the present invention, the wormgear being shown in section. The view also shows a helical member on which the production and the tooth shape are based.

Fig. 2 is a fragmentary front elevational view corresponding to Fig. 1, looking along the wormgear axis, and a diagram showing the mesh.

Fig. 3 is a section taken at right angles to the worm axis and containing the wormgear axis, corresponding to Fig. 1.

Fig. 4 is a fragmentary and diagrammatic view along its axis of the basic helical member shown in Fig. 1.

Fig. 5 is a diagram illustrating conjugacy of the worm and wormgear with an external helical member and an imaginary counterpart internal helical member respectively.

Fig. 6 is a view similar to Fig. 1, showing diagrammatically a rotary tool in engagement with the wormgear. I

Fig. 7 is a View similar to Fig. 1, showing diagrammatically another form of rotary tool in engagement with the worm.

Fig. 8 is a front view, looking at the cutting face, of a reciprocatory tool, such as may also be used according to the present invention.

Fig. 9 is a similar front view of a tools of modified form.

Fig. 10 is a diagrammatic plan view, looking along the center line, and partly a section, of another form of worm gearing, and a mesh diagram on which the production is based. A wormgear with helical teeth meshes with an enveloping worm, which is to be produced according to the invention.

Fig. 11 is a plan view and mesh diagram of an involute helical worm meshing with a wormgear shown in section, where the wormgear is to be produced with a standard tool rather than with a hob representing the worm.

Fig. 12 is a plan view and mesh diagram showing a helical gear and an enveloping worm conjugate thereto, to be produced according to the invention. Here the shaft angle dilfers from a right angle.

Fig. 13 is a diagram explanatory of a principle of feed control used in the present invention.

pair of reciprocatory Figures 14 and 15 are front views of a control member,

in two different turning positions, and of associated parts,

for controlling the varying-ratio straight-line feed, and

embodying the principle illustrated in diagram Fig. 13.

Fig. 16 is a fragmentary top view corresponding to Fig. 14 and showing levers used in the feed control.

Fig. 17 is a cross-section Fig. 16.

Fig. 18 is a longitudinal section of the narrow slide 132 used in connection with the control member of Fig. 14.

Fig. 19 is a diagram of a servo mechanism used with the controlmember of Figures 14 and 15.

Fig. 20 is a detail view of a slight modification of pin shown in Fig. 16.

Figures 21 and 22 are front views, in two different turning positions, of the control member of Figures 14 and 15 set up for a difierent kind of a job.

Fig. 23 is a similar front view showing a cam secured to the control member, and its connection with the lever 138 also shown in Figures 14, 15, 16, 21 and 22. f

Fig. 24 is a diagram of a general form of servo mecha nism different from the mechanism shown in 'Fig. 19.

taken along lines 17-17 of Fig. 25 is a plan view, and a section along broken lines 25-25 of Fig. 26, of a machine constructed according to the present invention.

Fig. 26 is a front elevational view corresponding to Fig. 25, an overhead drive being shown partly in section.

Fig. 27 is a cross-section containing the feed axis, of this machine, and a view of the work head and adjacent frame portions.

Fig. 28 is a diagram of a feed motor and of the disposition of the adjacent gears.

Fig. 29 is a drive diagram in perspective, somewhat exploded, of the machine shown in Figures 25 to 27, some parts being shown in section.

Fig. 30 is a diagram of the feed train of said machine, in perspective and slightly exploded.

Fig. 31 is a section showing a tool head with a tool of gear form, to be used on the machine illustrated in Figures 25 to 30 in place of the tool head that mounts a hob. The sectional plane contains the tool axis and the adjustment axis of the tool head. 7

Fig. 32 is a sectional view of a tool head mounting a pair of reciprocatory tools, to be used on the same machine in place of other tool heads. The sectional plane contains the adjustment axis of the tool head.

Fig. 33 is a sectional view taken at right angles to Fig. 32, the sectional plane containing the adjustment axis of the tool head and the directions of tool travel.

Fig. 34 is a fragmentary view corresponding to Figures 32 and 33, taken in the direction of the adjustment axis of the tool head. It shows the cam drive for reciprocating the tools.

Figures 1 to 7 refer to the production of an enveloping worm gearing disclosed in my aforesaid application. The worm gearing shown comprises an enveloping or throated worm 21 having its throat at 22 (Fig. 1), and a mating wormgear 23 having a root surface of concave profile 24 in axial section. The worm and wormgear are rotatably mounted on axes 25 and 26 respectively.

The threads 28 of the worm 21 are formed conjugate to the teeth 47 of a helical member 30 with axis 33. The teeth 47 have involute helical tooth surfaces 31 whose profiles 32 in any plane perpendicular to axis 33 are involutes of a base circle 34 with radius c (Fig. 4). Member 30 is so determined that at each turning position its tooth surfaces contact the worm threads 28 along the same lines along which the worm contacts its wormgear. In other words, member 30 is a basic member.

To be a basic member, its axis 33 should intersect the center line 36 of the worm gearing. As known, center line 36 intersects both axes of the wormgear pair at right angles. Furthermore the angular setting g (Fig. 1) of axis 33 to the direction of the worm axis.25 should have a definite relation to the offset 39-42 (Fig. 3) of axis 33 from the wormgear axis 26.

The said relation can best be expressed geometrically, by considering any plane perpendicular to axis 33 and offset from the center line 36. One such plane is projected into line 43:44-45 in Fig. 1. This plane intersects the worm axis 25 at 44a (Fig. 4) and the wormgear axis 26 at 45a. The axis 33 of a basic member should pass through the connecting line 44a-45a.

It can be demonstrated mathematically that this general relationship can be expressed with a simple formula When the axes 25 and 26 of the worm and wormgear are at right angles. Let C denote the center distance, that is the distance 41-42 (Fig. 3) between the intersection points 41, 42 of the center line 36 with the axes of the worm and wormgear. And let E denote the olfset of axis 33 from the wormgear axis 26, that is distance 39-42. Then helical member 30 matches the lead angle of the worm. POlIlt 40, the pitch point, is a point of the surface of action and its extension, on each of the two sides of the teeth. A plane 37 (Fig. 2) laid through pitch point 40 at right angles to center line 36 intersects the extended surface of action in a line 35 (Fig. 1), the path or extended path of contact in plane 37. This path can be shown to be a straight line. It is inclined at an angle 1' from the direction of the worm axis 25 and contains point 40' of the connecting line 44a-45a (Fig. 4). This permits geometric construction and computation of the inclination i of path 35, see also application Serial No. 701,792.

When the axes 25, 26 are at right angles, this general relation can be expressed by the simple formula tan i-tan g=i- Herein r and R are the pitch radii 40-41 and 40-42 respectively.

As the helical member 30 contains involute tooth surfaces, any surface normal at a point of contact remains a normal at all turning positions of member 30. Thus it continues to fulfill the condition of contact and lies in the surface of action. The surface of action of the considered side of the teeth is the surface containing all the normals to the involute helicoid 30 that intersect path 35. 5t}, 56, 50" are such normals at points 40, 40 and 40" of path 35 respectively.

Worm gearing of this kind has a very intimate tooth contact. It can be demonstrated that at pitch point 40 and at any point of normal 50 it is almost surface contact. In any section through such a contact point the sectional profiles of the wormgear tooth and worm thread are a concave curve matched by a convex curve of equal curvature. Such excellent contact however alsohas its danger of tooth interference. Indeed normal 58 marks one end of the useful surface of action. The latter contains all the normals 50, 50, 50" etc. within the boundaries of the outside surfaces of the worm and wormgear, that intersect the part of path 35 shown in full lines. This part ends at pitch point 40.

The contact at points 40', 40" and at points of their normals 50, 50 is also intimate, but without completely matched curvatures.

The opposite side of the teeth is identical with the described side, and can be made to coincide with it by turning the wormgear pair about center line 36 through half a turn.

Interference is avoided by a relief provided on the worm threads, starting at line 52 (Fig. 2) and increasing towards the adjacent end 55 or 55 of the worm threads. The thread side 53 contains a relieved portion 54. Similarly the opposite side 53' has a relieved portion adjacent end 55. Because of this relief the working portion of a wormgear tooth also ends at the line corresponding to normal 50 (Fig. 3). The dotted portion above and to the left of this line has no contact.

Pitch point 40 is preferably placed near the top of the worm threads to attain a large working portion. The mean path of contact thus obtained is shown in dotted lines 57 in Fig. 1.

While the worm 21 is conjugate to helical member 38 as in an angular worm drive, the wormgear 23 is con jugate to the side surfaces 31 of the helical teeth 47 in a different way. It can be considered conjugate to the side surfaces 31 of an internal member 30 (Fig. 4) that completely matches the external member 30. However such contact can only be imagined. It is not physically feasible as the diameter of such internal member is smaller than the diameter of the wormgear. The inside diameter of internal member 30 is smaller than the minimum root diameter at the throat of the wormgear 23. Also the concave tooth profiles of internal gear member 30' are more curved than the corresponding sectional profiles of the wormgear teeth. But although such contact is imaginary, it can be and is made the basis of production according,

to tire present invention, as it completely describes the mes Fig. 5 illustrates this kind of conjugacy. Section lines are omitted for convenience. The convex profile 61 of a wormgear tooth contacts the concave profile 60 of the mating worm thread in normal manner at point 40. The profile 62 of internal helical member 30' is more curved than profile 61. As it is concave it would interfere with profile 61 if the complete profile were physically embodied.

In accordance with my invention only the contacting points of the helical tooth surface of internal member 30' are embodied by a tool. Thus the tool does not represent and describe the entire profile 62 in any one position, but only the instantaneous contact point 40 thereof. And the tool is caused to follow the contact.

Fig. 6 shows how this may be done with a helical hob 70 with axis 71. In principle, this hob has an involute helical thread, capable of meshing with the plane side of a rack. However a common thread with straight profiles 72 in axial section differs only immaterially from it and may be used as well on single-threaded hobs. In the central position shown the involute helical hob thread meshes with the wormgear to be produced along a line of action that coincides with the surface normal 50. As the hob and wormgear turn on their axes in timed relation, an instantaneous contact point moves along line 59 and describes this line of the surface of action, thereby producing a corresponding line on the tooth surfaces of the wormgear.

Other lines are produced by displacing the hob relatively to the workpiece, so that it describes other lines of action, such as normal 50'. Like all other normals of the involute helicoid, normal 50 has the same inclination to axis 33 as normal 50 and is tangent to the cylindrical base surface that contains base circle 34 (Fig. 4). It passes through point 40' of path 35 and intersects the pitch cylinder 69 of helical member 30 or 30' at a point 73 (Figs. 4, 6). This point is displaced angularly about axis 33 from point 40, being turned through an angle a. Point 73 is also displaced in the direction of axis 33 with respect to point 40, as clearly seen in Fig. 6.

To describe normal 50 of the considered side of the teeth, the helical hob 70 is fed angularly about axis 33 through said angle u, and is fed along axis 33, relatively to the workpiece 23, a distance equal to the axial displacement of point 73 with respect to pitch point 44 Dotted lines 70' show the outside surface of the hob in this position, the hob axis being at 71. Simultaneously with these two feed motions the timing between the hob and workpiece 23 is changed to maintain the hob thread in contact with the helical tooth surfaces of member 30 which the hob successively describes. The timing change is in proportion to the angular feed and in proportion to the varying axial feed. The two proportions are generally different.

If u denotes the angular pitch of the helical member, that is 360 degrees divided by its tooth number, and 2,, denotes its axial pitch, the pitch in an axial plane, then the timing change due to an angular feed of u degrees is p pitches or teeth.

And the timing change going with an axial feed X is pa. pitches or teeth.

The total timing change in the algebraic sum of the above two changes.

In the central position of the hob, the hob axis 71 intersects the center line 36 of the wormgear pair. A line then coinciding with the center line but moving with the hob axis remains at right angles to axis 33 and to the hob axis. It intersects axis 33 at 63 and the hob axis 71' at 64. The axial displacement X is also equal to the projected distance 4'0,63, Fig. 6.

In one procedure the two sides of the teeth ar completely cut one after the other. On each side all the surface normals are successively described within the, tooth boundaries, that intersect the path of contact 36 in the portion shown in full lines and in the portion shown in dotted lines as well. The hob thread is then preferably made thinenough so that it touches only one side in each operation.

The angular feed of the hob about axis 33 is preferably made at a uniform rate. As will be further shown hereafter the feed along axis 33 is timed to said angular feed at a varying ratio. While it varies, it is continuously in one direction in this embodiment, during angular feed in one direction. V

In a preferred procedure the lines of action (50", 50', 50 etc.) of one side of the teeth are first described up to line 50 at the middle position, starting at the outer end of the full-line portion of path 35. The working portions of said one side are then completely formed. A standard hob is used that contacts both sides of the teeth in said middle position. As the angular feed goes on the axial feed required on the opposite side of the teeth is provided from the middle position to the opposite end position. Thereby the working portions of the opposite tooth side are produced.

The exact shape of the non-working or idle portions is immaterial, as long as it does not project beyond the theoretical shape. It may be relieved if convenient. And this is what occurs in the described preferred procedure The feed motion used on the idle portions fits the opposite side and differs from the theoretical feed motion in the axial feed. Increasingly difiierent axial feed positions are used with increasing turning angle u from the middle position. Contact with the helicaltooth surfaces of the imaginary member 30' is made at points ofa line of action offset from the theoretical line of action. Because the tooth surfaces of the imaginary internal member 30 interfere with the gear-tooth surfaces anywhere but at the theoretical line of action, more stock is removed than with the theoretical feed. In other words, the idle gear-tooth portion, shown with dotsin Fig. 3, is relieved. The described preferred process thus, finishes both sides of the wormgear teeth in a single operation, during continuous angular feed in one direction.

Any hob diameter'rnay be used up to a limit depending on the job. The hob should be small enough so as not to interfere with the gear tooth surfaces themselves. With the invention standard hobs may be used in a wide range.

Fig. 7 illustrates the production of the worm Zlof the described embodiment with a standard tool 75, which is a gear-shaped tool of disk form. A tool of this type is further shown in Fig. 31. In operation it turns on its axis 76 in time with the rotation of the workpiece 21. It is similar to a Fellows-type gear-shaper cutter, and indeed a rotary tool identical with said cutter could .be used, v

if desired. Tool or cutter 75 differs therefrom in that cutting clearance is attained by the position of the tool. This lets us use a cylindrical outside surface 77 on the tool, rather than a conical one. The tool diameter is thus unaffected by sharpening. Tools of this type are known.

In the central position shown in full lines the cutting edges 78 of tool 75 describe the line of action 50 of the thread sides particularly considered, and the lineof action of the opposite thread side, both lines of action passing through pitch point 40. They describe the same lines of action as hob 70 does in its central position. The feed between tool 75 and workpiece 21 is about and along the axis 33, exactly as described for ho-b 70 and the wormgear 23. V

Dotted lines 75', indicate a tool position where the line Y of action 50 is described by the rotary tool. Its axis 2 is then at 76'. The axial feed is timed to the angular feed about axis 33 at the same varying ratio as described, and the timing between the tool and workpiece is also changed at a varying rate as compared with the angular feed motion. It is changed in the same proportion to the pitch as already described.

When the described preferred procedure is used on worm 21 the working portions of both sides of the worm threads are produced in one operation, during continuous angular feed in one direction. But the idle portions 54 (Fig. 2) are not relieved in this first operation because of the conventional kind of mesh between the helical member 30 and the worm 21. This member is here an external member rather than an imaginary internal member.

Relief may be applied either in a second operation, or in an operation performed during the return feed. In this operation the same feed motions about and along axis 33 may be gone through, as described, but the timing change may be at a different rate.

Cylindrical hobs 70 and rotary gear-shaped tools 75 of disk form represent only two forms of tools that may be used. A reciprocatory rack-shaped tool 80 is shown in Fig. 8. Its straight cutting edges 81 describe a line of action (50, 50 etc.) as the tool is reciprocated side-wise at a uniform rate in the drawing plane of Fig. 8, while the workpiece rotates uniformly on its axis. At the end of each working stroke the tool 80 is withdrawn completely from the workpiece for a return stroke entirely clear of the workpiece which goes on rotating. Prior to the workin stroke the tool is again advanced to cutting position. The working stroke may extend through one pitch only.

Such a tool may be used in the embodiment of Fig. 6 for instance. In the middle position the tool 80 moves in the drawing plane of Fig. 6 in a direction to describe line of action 50, which is also described by bob 70. The feed motions and timing changes are the same as described for hob 70.

Fig. 9 shows a pair of tools 82, 82' that reciprocate along the lines of action 50x, 50x, in the direction of arrows 83, 83, during cutting while the workpiece rotates. They have convex cutting edges 84, 84' and can be used also on workpieces that have concave profiles. In some applications the cutting edges 84, 84' may each be replaced by a diamond point or the equivalent thereof. The tools 82, 82' also are completely withdrawn from the workpiece during the return strokes.

With either kind of reciprocatory tool the complete stroke cycle should occupy an inte ral number of pitches, which number should be prime to the tooth number of the workpiece. When this requirement is fulfilled the workpiece may be rotated uniformly in the entire process. Otherwise additional and intermittent indexing is required between successive stroke cycles.

In the described embodiment the axis 33 of the basic helical member intersects the center line 36 between the pitch point 40 and the wormgear axis 26. Other embodiments are also feasible, where the axis of the basic member intersects the center line between the pitch point 40 and the worm axis 25. Such an embodiment has been described in my aforesaid application. The described principles and procedures may also be applied to such embodiments. They may also be applied to angular worm drives, where the shaft angle differs from a right angle.

Fig. 10 refers to a right-angle drive where the wormgear 23]: is a helical gear with teeth whose side surfaces 86 are involute hel coids. Here the path of contact 35 through pitch point 40 extends at right angles to the wormgear axis 26 and parallel to the worm axis 25. as known. It re resents the instantaneous axis of a rolling motion in which the helical gear 23h moves axially without turning, like a rack. The surface of action contains all the normals 50, 50a. 50b etc. that intersect path 35' and lie between the outside surfaces of the worm ear and worm. These normals are the lines of action, as before. To pro- 8 duce the enveloping worm 87 we make use of the mesh between the worm and the helical member 23h. This basic member here coincides with the wormgear. Its cylindrical pitch surface 89 passes through pitch point 40.

Normal 50a passes through point 40a of path 35' and intersects the cylindrical pitch surface 89 at point 83a. Normal 50b at the opposite side of pitch point 40 passes through point 40b of path 35' and intersects the said pitch surface at 88b. The points 88a, 88b are here displaced to the same side axially of member 23/1 with respect to pitch point 40.

To cut worm 87 a suitable generating tool is provided, a tool like tool (Fig. 7) or a reciprocating tool 82 (Fig. 9). It is positioned to describe the line of action 50 in its middle position, while the worm to be cut turns on its axis in time with the tool motion. The tool is fed angularly about the axis 26 of the helical wormgear 23h. Simultaneously straight-line feed in the direction of axis 26 is effected between the tool and the worm being cut, in time with said angular feed and at a varying ratio thereto, in such a way that the pitch point of the tool passes through positions 88a, 40, 88b and describes line 9t) on which said points lie. At the same time the timing between the tool and workpiece is changed in proportion to the angular feed and also in proportion to the axial feed, to maintain the tool in contact with the helical tooth sides of the rotating wormgear which the tool represents. The said proportions are as described with respect to helical member 30.

Because the axial feed is at a varying ratio to the angular feed, the resultant timing change is at a varying rate. It should also be noted that during angular feed in one direction, from one end position to the opposite end position, the axial feed reverses in the middle position, at pitch point 40.

An entire feed pass is required to complete one side of the worm threads. The opposite side corresponds to a line 90 identical with line 90, and may be out either in a separate operation or during the return angular feed. This will be further described hereafter. Here also standard tools are used which have a wide range. Hitherto special tools were required that directly represented the helical wormgear and had approximately its diameter, its tooth number and its lead.

An application to cutting right-angle worm drives with helical worms will now be described with Fig. 11. Worm 91 contains multiple helical threads whose side surfaces are preferably involute helicoids envelopable by a plane. Its axis 25 is at right angles to the direction of the axis 26 of the wormgear 92. The wormgear 92 shall be cut with a standard tool.

What kind of tool to use depends on the design of the wormgear, and particularly on whether it contains concave tooth profiles depthwise of the teeth. Frequently it does not have any to speak of. Then a single-threaded hob like hob 70 may be used, or also a tool like tool 80. Otherwise a rotary cutter like cutter 75 of Fig. 7 or reciprocatory tools 82, 82' (Fig. 9) may be used.

A helical worm meshes like a rack with its wormgear. There is an instantaneous axis 93 that passes through pitch point 40 and is parallel to the wormgear axis 26. 93 is also the path of contact in a plane perpendicular to the center line through point 40. All the normals at points of contact between the Worm and wormgear intersect path 93. With involute worm threads the normals 50d, 50, Stle etc. at points 40d, 40, 40a of path 93 are also lines of action of the considered side of the teeth. They intersect the cylindrical pitch surface of the worm at points 94d, 40, 94a respectively of a line 95. The opposite side of the teeth has a similar intersection line 95', shown in dotted lines.

To cut one side of the wormgear teeth, the generating so that the tool body follows line 95 on the cylindrical pitch surface of the worm, and the tool successively describes all the lines of action of the surface of action. The axial feed along axis 25 is seen'to have a varying ratio to the angular feed about axis 25. It reverses in'the mid-position during angular feed in one direction. Simultaneously with these feeds the timing is changed in the manner described to maintain the tool in contact with the worm it represents in the complete process. The opposite side of the wormgear teeth may be cut during the return angular feed.

Fig. 12 relates to an angular worm gearing where the axis 97 of the worm member 98 includes an angle other than a right angle with the direction of the axis 99 of the wormgear 100. The latter contains involute helical teeth 101.

The worm member 98 may be embodied as an enveloping rotary lap or also as a grinding member. In either case it has a long contact with the helical teeth 101 it is to finish, so that the teeth tend to be rapidly equalized and corrected even without positive timing. For such applications worm members with a single thread or with two threads are preferred.

50 again denotes the tooth surface normal at pitch point 40. At this point the worm thread matches the direction of the gear teeth 101. The angular setting of the axis 97 can be determined in known manner as if member 93 had a helical thread of constant lead. Next we determine the straight path of contact 102 in a plane perpendicular to the center line and passing through pitch point 40, in the drawing plane of Fig. 12.

A plane 103 perpendicular to the axis 99 of helical gear 100 intersects axis 99 at a point 104 and the axis 97 at a point 105. The connecting line 104105 in space intersects the drawing plane at a point 106. The straight path of contact 102 is obtained by connecting the points 40 and 106. The surface of action of one side of the teeth contains the surface normals 50 50, 50g etc. that intersect path 102 at points 40 40, 40g respectively. As known, the said normals are tangent to the cylindrical base surface of the involute helical gear 100 and include a constant angle with its axis 99. The cylindrical pitch surface of gear 100 contains pitch point 40. The said normals intersect the pitch surface at points 110 40, 110g etc. that define a curve or line 108. The opposite side of the threads or thread has an identical line 108 on the pitch surface of the gear.

The two thread sides of Worm member 98 are cut one side after the other while feeding the tool about and along axis 99 so that the tool bodily follows line 108 and line 108' respectively, while the timing is changed in accordance therewith, so that the Working portion of the tool stays on the helical tooth surfaces it successively describes. For truing laps and grinding members I may use diamond-tipped tools or their equivalents, of the reciprocatory type shown in Fig. 9.

The axial feed We have described and defined the axial feed geomet= rically. It will now be expressed algebraically with formulas; and means will be disclosed for attaining it mechanically without special parts, or with parts that have a wide range of use.

The formulas below apply broadly to the feed about and along the axis of a member having involute tooth surfaces or thread surfaces, ordinarily a helical member of constant lead, and also to the special case of feed about and along the axis of a circular rack having conical'tooth sides of zero lead. They apply when the said member is a basic member different from either member of the wormgear pair, like for instance member 30 and counterpart 30 of Figures 1 to 7. And they apply also when the member is one of the two members of a wormgear pair, as for instance wormgear 23h of Fig. 10, worm 91 of Fig. 11, gear member 100 of Fig. 12.

1 0 We shall make use ofth angle k= (g-i) (Fig. 1)" between the path of contact 35 and the direction of the axis 33 of the helical member 30; of its transverse pressure angle p, at the pitch point 40, that is the inclination of the normal 50 at said point as it appears in projection (Fig. 4), looking along the axis 33 of the helical member 30; and of the base helix angle h which is also the constant inclination of the normals (50, 50', 50") to a plane perpendicular to the axis 33 of the helical member 30. We shall further make use of the pitch radius R of the helical member, which in Fig. 4 is radius 3340. R is broadly the distance of the pitch point 40 from the axis 33 of the helical member.

k and R may be determined as described. p and 11,, may be determined from the design data in known manner.

The axial feed X between pitch point 40 and any point '73 (Figs. 4, 6 and 7) is made up of two portions, of the axial component of distance 40-40, and of the axial component of distance 40'-73. They both depend on the turning angle u (Fig. 4). It can be shown that dis tance 4040 in the projection of Fig. 4 amounts to 00s z t- (m+ A R Sin (pt+ and that its axial component is A ctn k.

In the projection of Fig. 4 the distance B=40'73 can be shown to amount to 1-cos u B=R T hem (raw) and its axial component is B tan h The axial feed X can therefore be expressed as X=A ctn k+B tan h, 0)

This formula can be simplified with the use of a constant C and a constant angle q:

tan h tan is tan q: ctn p This is our basic formula. It shows how the axial feed X depends on the angular feed u.

In the more special cases illustrated in Fig. 10 and in Fig. 11 angle k is seen to be degrees. Hence tan q= infinity, q=90 degrees; C=R tan h In this special case Formula 3 can be transformed into S111 (In-P (3&)

for k=90.

A way of producing X mechanically will now be disclosed. Diagram Fig. 13 shows a radius 121 inclined at an angle p from the horizontal. A line 119 is drawn through point 121 at right angles to radius 120-- 121, and a point 122 is located thereon such that angle 12012212;1 equals the above angle q. Then a vertioal line 123 is drawn through point 122. When now radius 120-121 and line 119 together are turned about center 120 through any angle u, line 119 remains tangent to a circle 124 about center 120, and its intersection point with vertical line 123 moves from 122 to 122'. In the new position line 119 includes an angle (pH-u) with the vertical line 123, as does parallel line 120-125.

When distance 120-122 is made equal to C of For- 11 mula 2, the displacement X'=122122' can be shown to be When distance 120-122 differs from C, X is proportional to X and needs only a change of scale to be equal to X.

This is made use of in accordance with the invention. Figures 14 and 15 show a control member 130 mounted to turn about a center 120. Fig. 14 shows the control member in central position, while Fig. 15 shows it turned from the central position through an angle u about center 120. Member 130 may be turned by a worm 319.

Point 122 of Fig. 13 is embodied in Fig. 14 as the center of a pin 131 or roller mounted on a narrow vertical slide 132. A guide part 133 with straight guideway 134 is rigidly secured to control member 130, for engagement with pin 131. It is secured thereto by screws 135 that engage T-slots 136, 137 provided on member 130. Guide part 133 is located on member 130 from the pin 131 and from a guide pin 138, whose offset from a central pin 140 may be gaged. In the central position of the control member (Fig. 14) pin 131 is at the inner end of guideway 134, and part 133 is set so that the guideway extends in the direction of line 119 also shown in Fig. 13.

When now the control member 130 is turned through the angle u on an axis passing through center 120, pin 131 enters guideway 134 (Fig. 15) which moves the pin and slide 132 downwardly to a position 122 of the pin center. The vertical displacement of slide 132 is the same as distance 122-122 of diagram Fig. 13. This goes on for all turning angles 11 within range.

According to the described preferred method of cutting wormgear 23 the axial feed X corresponds to one side of the teeth from an end position to the center position; and from then on to the opposite end position it corresponds to the opposite side of the teeth while the turning feed continues in the same direction. This is ac complished with a pair of guide parts 133, 133 symmetrical to one another and symmetrically positioned on the control member. The central position (Fig. 14) marks the change-over. As member 130 is fed about center 120 in clockwise direction pin 131 has entered guideway 134 while the pin 131 has left its guideway 134. In the positions downward from the central position pin 131 and guideway 134 control the motion of slide 132. In the positions upward from the central position pin 131 and guideway 134' control the motion, as required.

Pins 131 and 131 are adjustable on slide 132 towards and away from each other, by turning screw 127 (Fig. 18). This screw contains a right-hand portion 128 and a left-hand portion 128' engaging blocks 129 and 129' respectively.

At its upper end slide 132 contains a horizontal slot 136 engaged by a pin or roller 137 of a lever 138. Displacement of slide 132 turns lever 138 on its axis 140, whereby the pin center moves in a circular path 141. Lever 138 is secured to a shaft 142 (Fig. 16). A further lever 143 is secured to the same shaft adjacent the rear of a feed slide to be described hereafter. Lever 143 is shown in section in Fig. 17. It has a U-shaped crosssection within which a block 144 is adjustable lengthwise of the lever. Adjustment is by means of a screw engaging an internal thread provided in block 144. A pin 145 projects from block 144. Pin 145 is adapted to engage a slot 146 of said feed slide. A spring 147 may be used to keep the block 144 pressed against lever 143 to effect a friction lock.

The adjustment of block 144 is for the purpose of changing the scale of the motion provided by slide 132. The smaller the distance of pin 145 from the turning axis 140, the more the motion of slide 132 is reduced.

12 Servo-mechanism Preferably the pin 144 does not by itself drive the feed slide, but only serves to control the feed. In addition to controlling the axial feed, the timing has to be changed in proportion to this varying feed. It should be changed preferably in a gear train that turns much faster than the workpiece. To attain smooth operation with good control I use a servo-mechanism for the axial feed and the accompanying timing change.

Any suitable servo-mechanism may be used. A mechanism based upon electrical control will now be described with Fig. 19. One pole of a voltage source 150, such as a storage battery, is connected with the sides of a slot 146 that moves with said feed slide. The opposite pole is connected through a solenoid 151 and an adjustible resistance 152 to the outer rim of pin 145. The solenoid 151 acts on the stationary part of a magnetic circuit that includes a moveable part 153. Energization of the solenoid causes part 153 to be drawn to the right in Fig. 19, reducing the gap 154. An end plate 155 of a multiple-disk friction clutch 156 is connected with part 153 to move therewith axially of said clutch. The clutch disks run in thin oil. The clutch body is rotatably mounted in suitable bearings 157 and contains gear teeth 158 on the outside. These are engaged by a pinion 159 that imparts uniform motion to the clutch body. The latter transmits torque to the driven member 160 of clutch 156 increasingly with increasing axial pressure exerted on end plate 155 by part 153 of the solenoid.

Driven member 160 turns the feed screw through a wormgear reduction, so that ample frictional resistance is offered to its motion. If desired, a disk brake running in oil may be further secured to member 169, to exert a fixed brake load thereon. It takes a certain minimum torque to turn member 160. Before this torque is attained there will be complete slippage in the clutch. As the axial pressure on end plate 155 is increased the slippage is reduced and member 160 starts to turn.

The driving clutch body is rotated at a speed slightly exceeding the maximum speed required on driven member 160 on a given job.

Accordingly the feed will be operated when the solenoid 151 causes enough axial pressure, that is when there is enough current in the solenoid. Should the feed slide tend to move too fast, for instance upwardly, the pressure between the upper side 146' of slot 146 and pin 145 is decreased, so that there is more resistance in the electric circuit. The current decreases and with it the pressure in the clutch. Slippage increases and the feed rate decreases. Should the feed slide move enough to break contact between the upper side 146 of slot 146 and pin 145 then the pressure in the clutch ceases and the feed stops until pin 145 again catches up with side 146'.

Backlash is intentionally provided in the drive to the clutch through pinion 159. On reversal of the feed, of pinion 159 and of control member 130, the pin starts earlier and moves away from side 146' because of said backlash. Soon the pin contacts the lower side 146" of slot 146. Electric current energizes the solenoid and causes the clutch to operate, so that downward feed is eflected. The action is the same as described for upward feed.

Fig. 20 illustrates a design of pin 145 intended to give an increased resistance change for the same change in contact pressure, to add to the smoothness of operation. Its outer electrically conductive rim is not exactly a cylindrical sleeve, but is a sleeve of constant thickness and a very slightly concave outer profile 171. On light pressure only the ends 172 of the sleeve profile are in contact with a plane side of slot 146. As the pressure increases, the contact spreads. The changing length of contact produces more variation in electrical resistance.

13 The described feed control applies to embodiments where the varying axial feed keeps going in the same direction without reversal during angular feed in one direction.

A more general feed control will now be described, which is also applicable when the feed reverses.

General feed control Figures 21 and 22 show the described control member 130 set up with different guide parts 233, 233', in a central position and in a position turned therefrom. The shown guide parts are for an embodiment where angle k to 90 degrees. Here the axial feed X corresponds to Formula 3a. In this case the center 222 of pin 139 lies on a line 120-222 inclined at angle p from the horizontal. Line 219 is perpendicular to line 120-222 and inclined at the same angle p from the vertical. Guide part 233 has a plane guide surface 234 set parallel to line 219.

When control member 130 is turned on its axis (120) through any turning angle u from the central position, and the pin 131 is maintained in contact with guide surface 234, the slide 132 moves vertically. Its displacement can be shown to conform to Formula 3a. The proper scale is attained by adjusting block 144 (Fig. 16) on lever 143, as described.

Each of the two sides of the teeth (or threads) requires angular displacement of the control member to both sides of the central position. One side is produced by maintaining pin 13-1 in contact with guide surface 234 during angular feed in one direction. The opposite side may be produced during the return angular feed, by maintaining pin 131' in contact with guide surface 234'. Guide part 233 is symmetrical to guide part 233. Contact is maintained hydraulically, by admitting pressure fluid to one side or the opposite side of a piston 200 that is movable in a cylinder 201. The rod 2112 of piston 200 acts on lever 138, which in turn presses the slide 132 up or down as desired. The pressure switches may be achieved automatically in known manner.

The same control member 130 may also be used in the modification shown in Fig. 23. Here a cam 250 secured to member 130 is used to actuate lever 138. The shown cam is for producing the same kind of motion as produced with the guide parts 233, 233'. It acts on a vertical slide 232 through a pair of diametrically opposite pins or rollers mounted on slide 232. The upper end of slide 232 contains a horizontal slot 236 engaged by a pin 237 of lever 138. Cams to represent Formula 3a have a wide range of application. A given cam can be used on all jobs, within machine limits, having the same transverse pressure angle p While I have shown straight pins and rollers in connection with the control member, conical pins or rollers may be used if desired.

Diagram Fig. 24 shows a servo-mechanism for general use. One pole of a voltage source 250 is connected with the outer rim 145' of pin 145 through an adjustable resistance 252. Slot 246 is part of the feed slide. Its sides 246', 246" are electrically insulated from each other. The upper side 246' is connected with the other pole 249 of voltage source 250 through a solenoid 260. The lower side 246" is connected with pole 249 through a solenoid 261. Each solenoid controls a magnetic circuit. The movable elements of the magnetic circuits are rigidly secured together to form a part 262 movable in the direction of the axis of a combination friction clutch 263.

Energization of solenoid 260 tends to move part 262 to the right, while energization of solenoid 261 tends to move it to the left. The combination clutch 263 is built so that pressure to the right turns the driven clutch member 264 and driven shaft 265 in one direction, and that pressure to the left turns shaft 265 in the opposite direction. The clutch housing consists of two symmetrical parts 266, 267, coaxially mounted in suitable bearings. They are turned in opposite directions by a bevel pinion 270 that engages opposite ring gears 271, 272 secured to the parts 266, 267 respectively. The driven clutch member contains friction disks 273 part of which engage adjacent disks of part 266, at the left, and part of which engage adjacent disks of part 267, at the right. When part 262 is pressed to the right, it applies pressure to the disks at the right, and tends to turn shaft 265 in the turning direction of gear 272. Pressure to the left tends to turn shaft 265 in the opposite direction. The disks run in thin oil for smooth operation.

Increased pressure at the upper side 246' of slot 246 thus operates to turn shaft 265 in one direction, in a direction geared to move the feed slide up. Increased pressure at the lower side 246" moves the feed slide down. In other words the feed slide follows the pin 145. In this way the required feed is attained and ample turning motion is produced to operate the feed and to change the timing in accordance therewith. In this general embodiment the bevel pinion 270 is rotated in one direction only regardless of the direction of the angular feed.

Machine Feed is about and along an axis, which represents the axis of the described helical member. This axis is preferably kept vertical, and preferably the angular feed about said axis is performed by the tool, while the straight-line feed in the direction of said axis is performed by the workpiece.

Figures 25, 26 and 27 show a machine of this kind. Fig. 29 is its drive diagram, and Fig. 30 shows its feed train. In an endeavor to point out the invention rather than to reflect the state of the art, the figures are held somewhat diagrammatic. No auxiliary devices for loading and unloading are shown, although they may be used if desired. Adjustment is illustrated by showing slides, but not the conventional adjustment means, as screws etc. For patent purposes adjustment could be made without such means. After adjustment the parts are rigidly secured together by conventional means not shown.

The machine 300 comprises a frame 301, a work head 36 2 and a tool head 303. The shown machine is set up for bobbing a wormgear 23 in accordance with Fig. 6.

A tool, here a single-threaded hob 70, is rotatably mounted in tool head 303. It may be adjusted in conventional manner in the direction of the hob axis. Tool head 303 is angularly adjustable on an upright 305 about a horizontal axis 3% (Fig. 25), and has a central guide portion 337. Upright 365 stands on a swing table 30 3 adapted to be fed angularly about a vertical axis 310, to achieve the described angular feed. The upright is radially adjustable towards and away from axis 310 along guide ways 311 of the swing table. Table 303 is rotatably mounted on .a slide 33-9 that is adjustable horizontally along guide ways 313 of the machine frame 391, to change its distance from the work head.

Upright 335 contains a vertical projection 314 for an overhead drive 315 to be discussed hereafter.

The work head 302 contains a work spindle 316 rotatably mounted therein and adapted to receive a workpiece 23. It is driven by a wormgear in casing 317. The work head is angularly adjustable about a horizontal axis 318 in a vertical feed slide 320. This slide is movable on the machine frame 301 along a pair of inserted guide parts 321.

In operation tool 70 and work spindle 316 are rotated in timed relation. The swing table 368 is fed angularly about its axis 310, preferably at a uni-form rate, and the feed slide 323 is fed along axis 310 at the described varying ratio to the angular feed.

The varying axial feed is controlled by a control memher 130 (Fig. 25), as described. Member 130 is preferably separate from the swing table 308, but duplicates its angular feed and reverses with it. It is rotatably mounted to turn on an axis 120 different from axis 310, and is driven by a worm 319 and wormgear 322 through the same angles as said angular feed. It is centered by a tapered bearing 333 that under load keeps it pressed against a ring-shaped plane bearing surface 334 of large diameter. In this way the wormgear 322 is as accurately and rigidly mounted as if it had a long shaft. A'similar kind of fiat mounting is used on the swing table 308 (Fig. 27).

Member 130 controls the operation of the feed screw 335 (Fig. 25) through a servo mechanism. Screw 335 engages a nut 336 rigidly secured to the feed slide 320.

The main drive is best seen in the drive diagram Fig. 29.

The hob 70 or tool is driven through a horizontal shaft 340 mounted in upright or column 305, through a pair of miter gears 341 and a helical pinion and gear 342. Shaft 340 extends along the adjustment axis 306 and contains a fly-wheel 343, shown in section. It may be driven from a motor 344 located in the upright 305 through compound change gears 345.

Shaft 340 also drives a vertical shaft 346 in projection 314. Shaft 346 is connected with another vertical shaft 350 through the overhead drive 315. Shaft 350 is rotatably mounted in the machine frame 301. The connection between shafts 346, 350 is through a pair of miter gears 347, 348, of which gear 347 is secured to shaft 346, and through a pair of miter gears 351, 352, of which gear 352 is secured to shaft 350. A guide part 353 pivots on the machine frame coaxially with shaft 350, at one end of the overhead drive. Part 353 is a full tube for part of the way and a tube segment 353 further on. At the other end of the overhead drive, segment 353 slidably passes through a head 354 that is mounted to pivot in the upright F coaxially with shaft 346. The guide part 353 is guided in head 354 and controls the direction of the overhead drive.

A hollow or internal member 355 is rigidly secured to miter gear 348, while miter gear 351 is rigidly secured to a shaft 356. A pair of coaxial rollers 357 are rotatably mounted on a radial axis at one end of shaft 356. The rollers 357 engage ways provided internally in member 355 and extending parallel to its axis. In line with the rollers 357 the hollow member 355 is supported in guide part 353 by a bearing 360.

I have gone to the described roller connection to assure smooth adjustment. This is here important because some adjustment takes place in operation. If desired, I may further use antifriction means for pivoting guide part 353 and head 354.

It should also be noted that the miter gears 347, 348 and 351, 352 are disposed to turn the vertical shafts 346, 350 in the same direction of rotation. If we consider miter gear 347, and for explanation assume it to be rigid with the upright while the angular feed about axis 310 goes on, the remaining miter gears 348, 351, 352 will turn. With the disposition illustrated miter gear 352 turns through the angle u of the uniform angular feed. This is readily taken care of in timing.

But with a miter-gear disposition such that the vertical shafts 346, 350 turn in opposite directions, the turning angle of miter gear 352 depends also on the inclination of the overhead drive. In general this inclination is not exactly proportional to the angle u, so that timing difficulties then arise.

Vertical shaft 350 is connected with a sun gear 361 of a differential 362 employed for timing control. The differential shown is of the spur-gear type, but a conventional bevel-gear differential could also be used. It comprises a sun gear 361, a sun gear 363 having a different number of teeth, and a planet carrier 364 with a planet 365 rotatably mounted therein. A single wide-faced gear or pinion 365 may be used to mesh with both gears 361,

16 363, provided that these have tooth numbers only slightly different. A wormgear 368 is rigidly secured to planet carrier 364 and meshes with a worm 369 of the feed train.

Sun gear 363 is connected with a vertical shaft 366 coaxial with shaft 350 and having a splined end 367. Rotatably mounted on a projection of the feed slide 320 are two miter gears 370, 371 coaxial with shaft 366. They both mesh with a miter gear 372 secured to a shaft 373 coaxial with adjustment axis 318. A toothed clutch collar 374 engages the splines 367 and permits to connect either gear 370 or gear 371 with shaft 366 by shifting the clutch collar. This causes rotation of shaft 366 in a direction selected according to the hand of the workpiece.

Rigid with shaft 373 is a cylindrical gear 375. it turns a worm 376 through a change gear 377 and an idler gear 378. The gears 375, 377, 378 may be spur gears or helical gears. Worm 376 rotates wormgear 380 and work spindle 316.

The gear ratios of the worm drive 376, 380 and the drive 342 of the tool are so determined that the tooth number of the change gear 377 is equal to the tooth number of the workpiece. or double its tooth number, if desired. With this tool head and single-thread hob only a single change gear is then needed in the main drive. The idler 378 does not have to be changed, but has to be shifted about gear 375 into mesh with change gear 377. It is rotatably mounted on a pin rigid with an adjustable ring 381.

The feed train The feed is preferably operated from a separate motor. Diagram Fig. 28 shows an arrangement using a constantspeed motor 400 driving a worm 401, a wormgear 402 meshing therewith, and a shaft 403, the latter through compound change gears 404 including an idler 404' shown in dotted lines. Shaft 403 drives a counter-shaft 406 selectively through a pair of gears 407 or a pair 408, 408, depending on the position of the clutch sleeve 410. The two sets of gears control the speed of the generating feed and the idle return feed. With the shown two pairs of gears a return feed about four times faster than the generating feed is obtained. The sleeve 410 is slidably splined to shaft 403 and is operated at the feed ends by automatic means not shown.

If desired, friction clutches may be used in place of the toothed clutches. This applies also to the clutch sleeve 411 that is splined to a shaft 412 coaxial with counter shaft 406 but separate therefrom. Sleeve 411 permits to couple shaft 412 either with the counter shaft 406 or with a miter gear 414. The latter meshes with a miter gear 415 secured to a shaft 416, and in turn meshing with a miter gear 413 secured to counter shaft 406. Shifting sleeve 411 reverses the rotation of shaft 412. Reversing shaft 412 is used to drive the .angular feed, while shaft 416 may drive a combination clutch 263 of a servo mechanism.

To finish enveloping members of the types described with Figures 10 to 12, the angular feed in one direction is used to finish one side of the teeth or threads, and the return angular feed to finish the opposite side. The angular feed then should be at the same speed in both directions. In this case the clutch sleeve 410 is left in one position and is not shifted. If such members are to be cut from solid blanks without previous roughing, the return feed may be faster than the first feed. To attain a return feed about twice as fast as the first feed, the gears 408, 417 are shifted axially on counter shaft 406, to which they are slidably keyed or splined, so that gear 417 engages gear 418. The latter is formed integral with gear 408, with which it may rotate on shaft 403 in an axially fixed position. The return feed is then through the gears 417, 418.

The feed train is shown in Fig. 30. Motor 400 drives a reversing shaft 412 and a non-reversing shaft 416. The

reversing shaft 412 drives a wormgear 420 through a worm 421. Wormgear 420 is secured to a shaft 419. A gear 422 secured to wormgear 420 meshes with a gear 423 journalled in the machine frame coaxially with a worm shaft 424. It has a sliding-key connection with shaft 424 to which worm 425 is secured. Worm 425 meshes with a wormgear or segment 426 that is part of the swing table 308, and effects the angular feed about axis 310.

The non-reversing shaft 416 drives a combination friction clutch 263 described above, through change gears 430, a bevel pinion 270 and two ring gears 271, 272. This clutch is part of the servo mechanism for effecting the varying feed of the vertical feed slide 320 and the timing change accompanying it. The driven shaft 265 turns at a varying speed through a considerable number of turns.

A worm 280 is secured to shaft 265 and drives feed screw 335 through a wormgear 281. Shaft 265 further drives a shaft 431 arranged parallel thereto through compound change gears 432. Only the first and last of these change gears are shown in full lines. The intermediate gears are here represented by an idler 432 shown in dotted lines, for convenience. Shaft 431 imparts turning motion to a sun gear of a differential 433, of either spuror bevel-gear type. The planet carrier thereof is formed integral with a gear 434 and receives motion from reversing shaft 412 through compound change gears 435, a shaft 436 and a pinion 437 secured to said shaft. Only the first and last gear of the change gears 435 are shown in full lines, while the intermediate gears are represented by an idler 435 shown in dotted lines. The rotational direction of the driven member can be reversed, if need be, by adding an idler (not shown) to the compound change gears 432 or 435.

The remaining sun gear of differential 433 is secured to a shaft 440, which imparts motion to Worm shaft 441 through two pairs of miter gears 442, 443 and a vertical shaft 444. Worm 369 is rigid with shaft 441 and meshes with the wormgear 368 of planet carrier 364. The latter is part of the differential 362 already described, see Fig. 29. I

The change gears 435 serve for changing the timing between the tool motion and Work spindle in accordance with the angular feed, as described. In computing them allowance is made for the described further turning motion of shaft 350.

The change gears 432 serve for changing the timing in accordance with the varying straight-line feed, the variation being reflected by the changing turning motion of shaft 265. The differential 433 combines the two changes in known manner.

Shaft 419 of wormgear 420 further imparts motion to the worm 319 selectively through a pair of miter gears 450, 451 or 452, 451 and a shaft 453. Worm 319 meshes with a wormgear 322 secured to the described control member 130.

The described feed train may also be used with the servo mechanism of Fig. 19 when shaft 416 adjacent feed motor 400 is made a reversing shaft, like shaft 412.

Other tool heads Other tools may be used on the described machine by substituting a different tool head for the tool head 303. Tool head 303' shown in Fig. 31 is for use of a gearshaped tool 75 of disk form, also shown in Fig. 7. 'It has the same angular adjustment about horizontal axis 306 as tool head 303. Tool or cutter 75 is secured to the tool spindle 500 that is rotatably mounted in tool head 303'. The spindle 500 is driven from a horizontal shaft 340 coaxial with adjustment axis 306, through a pair of miter gears 341 already referred to, through change gears 501 indicated by their pitch circles, and a worm and wormgear 502. The latter is secured to the cutter spindle 500. Spindle 500 is inclined from the adjustment axis 306 of tool head 303 at an acute angle in the design illustrated. a

Tool head 303" (Figs. 32, 33) mounts a pair of'r'eciprocatory tools 82, 82 shown also in Fig. 9. The two tools are rigidly secured to a pair of slides 510,510 respectively, that are movable in straight guide ways along 7 the slides 510, 510'. This engagement causes the slides 510, 510' to reciprocate in the inclined directions, of the guideways, along lines of action 50x, 50x, see Fig. '9, upon reciprocation of the driving slide 511. The said guide ways are formed at the rear by slide 511 and chiefly by a guide-part 514 shaped like a low V.

The driving slide 511 is moved in time with the work spindle during the cutting strokes. Its motion is derived from a rotary member 515, rotated from shaft 340 through miter gears 341, change gears 516 shown partly, and a worm and wormgear 517. Member 515 is rotatably mounted in the tool head 303" which is suitably split to permit assembly. A symmetrical cam 518 is rigid with member 515 and forms part thereof. It differs only moderately from a large-size crank pin, as best seen in Fig.

34, and engages parallel straight guide ways 520 of a swinging member 521 pivoted at 522. The center line of the'ways 520 is radial of the swinging axis. Rotation of member 515 and cam 518 reciprocates or oscillates member 521. The shape of cam 518 is so determined that during the working pass the trigonometric tangent of the turning angle u of member 521 is proportional to the turning angle u" of rotary member '515 tan u=Ku"; K=constant "can be changedby adjusting roller 526 on driving slide 511 at right angles to the slide travel. Adjustment towards pivot 522 decreases the tool travel, adjustment away from pivot 522 increases the tool travel, while keeping the speed uniform during the working portion of the cycle.

After each working stroke the tools are withdrawn from the workpiece, to be entirely clear of it during the return stroke. This motion, the clapping, is effected by a cam 530 rigid with rotary member 515. The cam periodically moves guide-part 514 in the direction of the adjustment axis 306 of tool head 303" through its engagement with a roller 531. The roller is rotatably mounted on a portion 514 rigid with guide-part 514 and together with it are guided by suitable guide portions, placed partly adjacent roller 531 and partly adjacent the tools 82, 82. The latter may take the form of a large key 532. Spaced stops 533, 533' are provided on the tool head 303", to rigidly hold the guide-part 514 during the working strokes of the tools.

In a modification, not illustrated, the driving slide 511 is reciprocated by a mechanism disclosed in my Patent No. 2,770,973, granted November 20, 1956.

Only the essentials have been described andshown in The parts may be mass-balanced and torque-balanced in accordance with the principles disclosed in my pending application entitled Inertia Member, filed March 14, 1955, Serial No. 494,076.

In addition to using a set of different tool heads on the described machine, the work head or part thereof may be changed for widely difierent applications. Thus for cutting or truing enveloping worm members having a single thread or only a few threads I preferably provide a worm 376 of large lead angle, or other gearing, to drive the wormgear 380 at a smaller reduction.

The method has been described particularly for achieving full tooth contact. Easeofi may be obtained on the teeth by departing very slightly from the described procedure, as practiced in the art with other methods.

In the specification and claims I have used the term teeth in its broad meaning, to include threads. Also the term cutting should include the action of a diamond in truing or dressing an abrasive member. The term helical is always used in its specific meaning. Thus a helical tooth is a tooth extending along a helix (of constant lead), that is along a line traceable by a point that moves about and along an axis, where the motion along said axis is at a constant ratio to the motion about said axis.

While the invention has been described in connection with several different embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains, and as fall within the scope of the invention or the limits of the appended claims.

I claim:

1. The method of producing the teeth and threads of enveloping members, such as wormgears, enveloping worms and the like, which comprises mounting a tool and a workpiece adjacent each other, imparting motion to said tool while turning said workpiece on its axis in timed relation to said tool motion to effect cutting, effecting angular feed motion between said tool and workpiece about an axis disposed at an angle to and offset from the axis of the workpiece, elfecting feed motion between said tool and workpiece in a straight path in time with said angular feed motion and at a varying ratio thereto, and changing the timing between said tool and workpiece at a varying rate as compared with said angular feed motion.

2. The method according to claim 1, wherein said tool is a single-threaded hob and the cutting motion is chiefly a rotation about the axis of said hob.

3. The method according to claim 1, wherein said tool is a rotary gear-shaped tool of disk form, and the cutting motion is composed of the rotational motion of the workpiece and the turning motion of said tool on its axis.

4. The method according to claim 1, wherein said tool is a reciprocatory tool that moves in a straight path, said path lying in a plane approximately perpendicular to the direction of the teeth being produced.

5. The method according to claim 4, wherein said tool moves in a straight path normal to the tooth surface being produced, while the workpiece turns on its axis.

6. The method of producing the teeth and threads of enveloping members, such as wormgears, enveloping worms and the like, each conjugate to tooth surfaces of constant profile of a cylindrical part whose axis is angularly disposed to and offset from the axis of the respective member, which comprises mounting a workpiece and a tool adjacent each other, imparting motion to said tool while turning said workpiece on its axis in timed relation to said tool motion to effect cutting while describing a line of action between the completed workpiece and said cylindrical part, effecting feed motions between said tool and workpiece about and along the axis of said cylindrical part to describe other lines of action between the completed workpiece and said cylindrical part, the feed motion along said axis being timed at a varying ratio to the feed motion about said axis, and changing the timing between said tool and workpiece at a varying rate as compared with the feed motion about said axis.

7. The method according to claim 6, wherein said cylindrical part contains helical tooth surfaces of constant lead.

8. The method according to claim 6, wherein said cylindrical part is a basic member adapted to contact the tooth sides of the enveloping member to be produced along the same lines along which said enveloping member contacts its mate, and wherein the axis of said basic member is angularly disposed to and offset from both the axes of said enveloping member and of its mate.

9. The method according to claim 6 wherein said cylindrical part is an internal member and has imaginary contact with said enveloping member, the inside diameter of said part being smaller than the minimum root diameter of said enveloping member.

10. The method according to claim 6 wherein the feed motion along said axis is continuously in one direction but at a varying rate during uniform feed motion about said axis in one direction.

11. The method of producing the tooth sides of a work piece conjugate to the tooth sides of an imaginary internal member of constant profile, said internal member having a smaller inside diameter than the minimum root diameter of the completed workpiece, which comprises providing a tool adapted to describe a line of action between said workpiece and internal member, said line extending in a general direction perpendicular to the tooth sides of said internal member, imparting motion to said tool to describe said line of action while turning said workpiece on its axis in time with the motion of said tool, to effect cutting, efiecting feed motions between said tool and workpiece about and along the axis of said internal member to describe other paths of contact, and changing the timing between said tool and workpiece.

12. The method of producing an enveloping worm conjugate to a wormgear having helical tooth sides and having its axis at right angles to the direction of the worm axis, which comprises mounting a workpiece and a tool adjacent each other, imparting motion to said tool While turning said workpiece on its axis in time with the motion of said tool, to effect cutting, effecting feed motions between said tool and workpiece angularly about and straight along an axis disposed at an angle to and ofiset from the axis of the workpiece, the last-named axis coinciding approximately with the axis of the helical wormgear, the feed motion along said axis having a varying ratio to said angular feed motion and having a reversal of direction as the angular feed motion proceeds continuously in one direction, and changing the timing between said tool and workpiece at a varying rate as compared with the rate of said angular feed motion.

13. The method of producing a wormgear conjugate to a helical worm having its axis at right angles to the direction of the wormgear axis, which comprises mounting a workpiece and a tool adjacent each other, impartingmotion to said tool while turning said workpiece on its axis in time with the motion of said tool, to effect cutting, eifecting feed motions between said tool and workpiece angularly about and straight along an axis disposed at an angle to and ofiset'from the axis of the workpiece, the last-named axis coinciding approximately with the axis of said helical worm, the feed motion along said axis having a varying ratio to said angular feed motion and having a reversal of direction as the angular feed motion proceeds continuously in one direction, and changing the timing between said tool and workpiece at a varying rate as compared with the rate of said angular feed motion.

14. A machine for producing teeth and threads on enveloping members, comprising a work spindle rotatably mounted in a work head, a tool movably mounted in a tool head, means for imparting motion to said tool, means for rotating said work spindle in time with said tool motion, means for effecting angular feed motion between said tool head and work head about a fixed axis, means for efiecting straight-line feed motion between said tool head and work head in the direction of said fixed axis at a varying ratio to said angular feed motion, and means for changing the timing between said tool and the work spindle at a rate which varies as compared with said angular feed motion.

15. A machine according to claim 14, having a rotatable control member for controlling said straight-line feed motion, a connection to turn said control member on its axis in proportion to said angular feed motion and to reverse with said angular feed motion, means for deriving straight-line motion from said control member in proportion to the required varying straight-line feed motion, and means for effecting said straight-line feed motion through said derived motion.

16. A machine according to claim 15, wherein said connection is such as to duplicate the angular feed motion, so that said control member turns simultaneously through the same angles as said angular feed motion.

17. A machine according to claim 16, wherein a guide part with a straight guide way is adjustably secured to said control member to form a portion thereof, for engagement with a part mounted on a slide that is movable in a straight path, to cause said slide to move in proportion to the required straight-line feed motion.

18. A machine according to claim 17, wherein a pair of guide parts are adjustably secured to said control member, for successive engagement with a pair of cooperating parts mounted on the same slide.

19. A machine according to claim 15, wherein a cam is rigidly secured to said control member, said cam being of disk shape and engaging a pair of diametrically opposite cooperating parts of a slide that is movable in a straight path, to cause a slide motion in proportion to the required varying straight-line feed motion, and means for changing the scale of one of said two motions to make them substantially equal and comparable being provided.

20. A machine according to claim 14, comprising further a control member for controlling the straight-line feed, said control member being rotatably mounted on an axis different from the axis of said angular feed, means for turning said control member on its axis in proportion to said angular feed to reverse with said angular feed, and means for deriving straight-line motion from said control member in proportion to the required straight-line feed motion.

21. A machine according to claim 14, comprising further a rotatable control member, a connection to turn said control member on its axis in proportion to the angular feed and to reverse it together with the angular feed, means for deriving varying straight-line motion from said control member in proportion to the required straightline feed motion, and means for changing the scale of one of said two motions to render them substantially equal and comparable.

22. A machine according to claim 14, wherein the means for effecting the straight-line feed motion of varying ratio comprise control means governing said feed 23. A machine according to claim 22, wherein the means for rotating the work spindle in time with the tool motion comprise a gear train with dillerential, and H wherein the rotatable shaft driven by the servo means is connected through change gears and further gears with said dilferential.

24. A machine for producing teeth and threads on enveloping members, comprising a work spindle rotatably mounted in a work head, a tool movably mounted in a tool head, means for imparting motion to said tool, means for rotating said work spindle on its axis in time with said tool motion, means for feeding said tool head angularly about a vertical axis, means for feeding said work head vertically at a varying ratio to said angular feed motion, and means for changing the timing between said tool motion and said work spindle at a rate which varies as.

compared with said angular feed motion and which depends on said vertical feed motion.

25. A machine according to claim 24, wherein said tool head is adjustably secured to an upright and said work head is adjustably secured to a vertical slide, ad justment of said heads being about two horizontal axes respectively.

26. A machine according to claim 14, wherein said tool is a rotary tool, wherein a tool spindle is provided for rotatably mounting said tool in the tool head, and wherein means are provided for rotating said tool spindle.

27. A machine according to claim 25, wherein the tool is a gear-shaped cutter of disk form, wherein a tool spindle is provided for rotatably mounting said cutter on the tool head, the axis of said tool spindle being inclined from the adjustment axis at an. acute angle, and wherein means are provided for rotating said tool spindle.

28. A machine according to claim 14, wherein said tool is reciprocatory tool, wherein means for moving said tool in a straight path approximately in proportion ot the turning motion of the work spindle are provided, and means for clapping said tool to keep it clear of the workpiece during the return strokes.

29. A machine according to claim 28 that contains a pair of tool holders, means for reciprocating said tool holders along straight lines angularly disposed to each other approximately in proportion to the turning motion of the work spindle during the cutting strokes, and means for clapping said tool holders to keep their tools clear of the workpiece during the return strokes.

30. A machine according to claim 24, wherein the timed rotation of the work spindle is eifected by a gear train with an overhead drive, said overhead drive comprising a rotary internal member with straight axially extending ways, an external member with rollers engaging said ways, and a guide part pivoted at one end of i said overhead drive and passing slidably through the other end, said guide part containing a bearing for said internal member intermediate the ends of said overhead drive.

References Cited in the file of this patent UNITED STATES PATENTS 1,965,002 Richer July 3, 1934 8 2,043,012 Schurr June 2, 1946 2,700,324 Staples et a1. Jan. 25, 1955 2,704,492 Sykes Mar. 22, 1955 2,731,886 Saari Jan. 24, 1956 2,847,910 Staples et al Aug. 19, 1958 

